This invention relates generally to a spark ignition device and more particularly to an encapsulated spark plug.
Emissions and efficiency continue driving technology to improve combustion of air and fuel mixtures. Many improvements have come by controlling the air and fuel mixture. These controls have come through improved design of combustion chambers, improved valving, improved control of fuel, and atomization of fuel. These improvements all generally improve control of the fuel and air mixture.
Unlike in a diesel cycle engines, spark ignited engines may also control a combustion event through initiation of a spark. Encapsulated spark plugs combine improvements gained by improving condition and mixing of fuel and air along with improvements gained by controlling initiation of the spark. An encapsulated spark plug includes a plug shell surrounding an electrode gap. The plug shell defines an ignition chamber separate from a combustion chamber. The ignition chamber also separates a flame kernel from turbulence in the combustion chamber. As a piston compresses an air/fuel mixture in the combustion chamber, at least a portion of the air/fuel mixture passes through orifices on the plug shell into the ignition chamber.
In the ignition chamber, a spark causes the portion of air/fuel mixture to combust resulting in a pressure rise in the ignition chamber. As the pressure in the ignition chamber overcomes pressures in the combustion chamber, hot gasses escape from ignition chamber forming multiple ignition into the air/fuel mixture in the combustion chamber. Multiple ignition torches increase combustion rates in the combustion chamber and reduce masses of unburned air/fuel mixture. Richardson shows encapsulated spark plugs in both U.S. Pat. No. 4,937,868 issued Jan. 29, 1991 and U.S. Pat. No. 5,105,780 issued Apr. 21, 1992.
Increased temperature environments experienced by encapsulated spark plugs tend to reduce their lives. Operation in a lean air/fuel mixture increases required break down voltages needed to jump an electrode gap between an electrode and ground electrode. Increased break down voltages requires a greater electrical insulation between the electrode and ground electrode. The increased electrical insulation often means increasing a heat transfer path between a capsule connected to the ground electrode and a cool environment. Further exacerbating wear, the orifices through the plug shell experience extreme temperature changes. Hot gas exits the ignition chamber through the orifices at high velocities. These high velocities increase heat transfer from the hot gases to the plug shell. However, resistance such as welds hinder heat transfer away from the orifices
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect the present invention includes a spark plug having an encapsulated electrode gap. The spark plug has an insulator. A spark plug shell has an insulator retention region, a connection region, an orificed region, and a tip portion. The insulator retention region connects with the insulator. The connection region is adapted to engage a cylinder head. The spark plug shell has a plurality of orifices. A first electrode connects with the insulator, and the insulator separates the first electrode from the spark plug shell. A second electrode connects with the spark plug shell. A plug shell cap connects with the spark plug shell adjacent the tip portion.
In another aspect of the present invention, a method of making an encapsulated spark plug includes forming a spark plug shell with a plurality orifices. A second electrode is connected to the spark plug shell. The second electrode is insulated from a first electrode. An electrode gap between the first electrode and the second electrode is adjusted through an access orifice of the spark plug shell. The access origin is then covered.